Cryogenic insulation system



Se t. 12,1967 c. o. FORMAN ETAL 3,341,050

CRYOGENIC INSULATION SYSTEM Filed Nov. 16, 1964 FIG. 1

- FIG. 2

GAS DETECTO'R I g I5 49 I 40 3| 34 30 46 p4 3o (35 47 4| .38 as 3y /47 Q m J 1 0 J v 39 39 j INVENTORS 2 CHARLES D. FORMAN AUGUSTUS B. SMALL PAUL T. GORMAN WHELAN, CHASAN, LITTON, MARX a WRIGHT ATTORNEYS United States Patent 3,341,050 CRYOGENIC INSULATION SYSTEM Charles D. Forman, Elizabeth, Paul T. German, Chatham,

and Augustus B. Small, Westfield, N.J., assignors to Esso Research and Engineering Company, a corporation of Delaware Filed Nov. 16, 1964, Ser. No. 411,527 8 Claims. (Cl. 220-9) ABSTRACT OF THE DISCLOSURE The cryogenic insulation system of this application is constructed from groups of prefabricated, dimensionally stable primary and secondary barrier panels connected side-by-side to define an inner and outer liquid-tight shell. In accordance with the disclosure, the prefabricated panels constituting the inner shell employ a material which has a very low coefficient of thermal expansion. The use of this material insures that the inner panels, though restrained, -will not be subjected to undue thermal stresses upon contact with the cryogenic cargo to be contained in the system.

The present invention relates to insulation systems and, more particularly, to integral insulation systems used in the storage and marine transportation of liquefied natural gas cargoes at atmospheric pressures under which conditions the liquefied natural gas cargoes are at cryogenic temperatures.

It has been established that the transportation of gases, such as natural gas, hydrogen, oxygen, methane, and the like, to remote locations, may best and most efiiciently be accomplished by reducing the volume of the gas through its conversion into the liquid state. Such a conversion enables the storage volume requirements to be greatly reduced (approximately six-hundredfold for a given quantity of methane gas, for example) and, as should be appreciated, enables the most efiicient transfer of the gas to a remote area.

In order to transfer liquefied gas in a practical and economical manner in relatively large volumes, it is necessary to store the liquefied gas at approximately atmospheric pressures, since large containers built to withstand superatmospheric pressures would be impractical, if not impossible, to construct for use on seagoing tankers or the like. However, liquefied gases maintained at atmospheric pressures have extremely low vaporization points, rainging from about -435 F. for liquefied hydrogen, to 28 F. for liquefied ammonia, and these unusually low temperatures of the liquids present certain problems in the design and production of insulated cargo containers. Specifically, the containers must be capable of preventing heat losses which would lead to subsequent volatilization of the stored liquefied gas and of withstanding the internal stresses that may be induced therein by the large temperature gradients through the outer relatively warm walls of the ship to the supercooled inner surfaces of the container.

Certain conventional arrangements for transportating liquefied gases have involved the use of an aluminum or a stainless steel storage tank constituting a primary liquidtight barrier independently supported within an insulated chamber and separated therefrom by a secondary liquidtight barrier, the requirement of two barriers being dictated by well accepted safety practices and the provisions of certain regulatory codes. Alternatively, so-called integral systems have been employed to achieve the same ends, in which the aforementioned primary and secondary barriers are directly superimposed and are supported by an enveloping structure, such as the walls of a cargo hold formed in a ships hull.

Due to the extremely low temperatures of the liquefied natural gases, the above-mentioned systems invariably include some form of mechanical compensation, usually in the nature of expansion joints, to accommodate the normally contractive effects of the supercooled cargoes on the container structure itself.

As an important aspect of the present invention, a new and improved cryogenic insulation system is provided which requires no mechanical expansion joints or the like. As a further important aspect of the invention, a cryogenic cargo container embodying the new and improved system is constructed from groups of prefabricated, effectively dimensionally stable primary and and secondary barrier panels. Superimposed end-to-end, side-by-side arrays of each group of panels define two distinct liquid-tight barriers. In accordance with the invention, these prefabricated panels may be mounted progressively and with relative ease to a supporting structure such as a tanker cargo hold to define a new and improved closed cryogenic cargo container.

More specifically, the panels comprising the secondary barrier are generally similar to the fiberglas reinforced polyester and polyurethane foam, thermal insulating panels first disclosed in the copending Harold R. Pratt et al. application Serial No. 394,287 filed Sept. 3, 1964, for Insulation System, and are effectively dimensionally stable, while in accordance with specific aspects of the present invention the primary barrier panels are in the nature of effectively dimensionally stable triplex panels formed by sandwiching a honeycomb core between spaced high nickel alloy steel sheets, possessing approximately 35.5 percent nickel and available commercially under the trade designation of Invar. The Invar sheets are held in a frame made of similar high nickel alloy steel. As will be appreciated, the utilization of efiectively dimensionally stable primary and secondary barriers obviates the need for sophisticated expansion systems, inasmuch as the new container undergoes no efiective or deleterious dimensional changes in use, although being subjected to cryogenic temperatures ranging as low as 260 F. during the loading and unloading cycles of the container.

As another aspect of the invention, the primary and second-ary barriers are integrally united by an intermediate liquid-tight barrier of epoxy adhesive thus providing a resultant structure having three liquid-tight barriers. It is to be understood that the importance of the impermeable barriers is to preclude cryogenic cargoes from contacting the supporting steel structure or ship hull and causing the embrittlement thereof. Likewise, it should be clear that the effectively dimensionally stable panels used in fabricating the new and improved cryogenic container are themselves non-embrittling, remaining relatively ductile at the supercooling temperatures of liquefied natural gases.

A further important aspect of the invention resides in the relatively high degree of fail safety obtained. The nature of the construction and superimposition of the primary and secondary panels, with an interposed liquidtight intermediate barrier, is such that a failure in one will not cause a failure in the other. Moreover, this high degree of fail safety is further enhanced by providing a new and improved leakage system which includes a unique gas detection network which is an integral part of the primary barrier. More specifically, each of the honeycomb cores and each frame member of the triplex panels defines a passage therethrough which is linked to the passage of adjacent panels. Tthe interconnected passages are in turn associated with a gas detector which continually monitors the detection network for the presence of gas, which is, of course, an indication of the development of a leak.

For a more complete understanding of the present invention and appreciation of its attendant advantages, reference should be made to the following detailed description taken in conjunction with the accompanying drawing, in which:

FIG. 1 is a cross-sectional view of an insulated container, embodying the concepts of the present invention in a cargo hold of a ship;

FIG. 2 is an enlarged fragmentary cross-sectional view, taken along line 2-2 of FIG. 1, showing details of construction of the new and improved integral insulation system for the transportation of cargoes at cryogenic temperatures at atmospheric pressures; and

FIG. 3 is a fragmentary perspective view of a new and improved, dimensionally stable, triplex primary barrier panel.

Referring to FIG. 1, the cryogenic insulation system of the present invention is directly and fixedly supported by the secondary insulating barrier and is characterized as an integral system. In the illustrated preferred embodiment, the supporting structure for a new and improved cryogenic cargo container 9 is the mild steel plate 10 of the cargo hold 11 of a dou-ble-hulled tanker 12. The integral insulation system includes a secondary liquidtight barrier in the form of a continuous thermal insulating layer 13 supported in an end-to-end, side-by-side relation by the inner hull structure 14 of the ship and a primary liquid-tight barrier 15 superimposed upon the secondary barrier 13 and directly, fixedly anchored thereto.

Specifically and as shown in FIG. 2, the continuous, effectively dimensionally stable, secondary barrier 13 is established by securing stepped insulating panels 16 through mounting flanges 17 extending peripherally outwardly from base portions thereof, to the inner hull plate 11 by means of a nut 18, a clamping washer 19, and a Nelson stud 20. Advantageously, the insulating panels 16 are generally similar to those dimensionally stable panels disclosed in more detail in the above-identified copending application of Harold R. Pratt et al. More specifically, the insulating panels 16 are approximately five feet by twentyfive feet in size, are generally symmetrical in shape (FIG. 2 showing opposite sides of two adjacent insulating panels), and include fiberglas reinforced polyester shells 21 filled with polyurethane foam 22. Each gap 23 formed between opposing faces 24 of adjacent insulating panels 16 is filled with a matingly stepped plug piece 25 having, similarly to the panels 16, a fiberglas reinforced polyester shell 26 filled with polyurethane foam 27 and being similarly effectively dimensionally stable.

The secondary barrier 13 defined by the end-to-end and side-'by-side array of insulating panels 16 and plug pieces 25, is made continuous and liquid tight by the bonding of the plug pieces 25 to the opposing stepped faces 24 of adjacent insulating panels by a suitable adhesive sealant 28. As set forth in more detail in the beforementioned Pratt et al. application, the above-described insulating secondary barrier 13 is effectively dimensionally stable and will not undergo deleterious contraction when subjected to the extreme temperatures (e.g., --258 F. for liquefied methane) encountered in the cryogenic environments of liquefied natural gases.

In accordance with the principles of the present invention, a cargo resistant, primary barrier is formed by a plurality of dimensionally stable triplex panels 30, each hav ing a generally rectangular shape defined by a peripheral frame member 31 fabricated from an extruded C-shaped channel having an outer flange 37 and an inner flange 38 connected by a web 39. As shown in FIG. 2, the triplex primary barrier panels 30 include inner and outer metallic sheets 33, 32, respectively, which, in accordance with the principles of the present invention are also made from a dimensionally stable metal and are welded or otherwise suitably united with the frame members 31. The sheets 32, 33 are maintained in a predetermined spaced relation, advantageously of approximately one-fourth to onehalf inch, and the panel 30 is strengthened by an intermediate honeycomb core structure 34 advantageously of phenolic-impregnated paper, fiberglas reinforced polyester, aluminum or the like. In addition to contributing to the strength of the thus formed triplex panel, the honeycomb core 34 enhances its insulating properties by providing dead air space 35 therein.

As an important aspect of the invention, the frame member 31 and sheets 32, 33 are fabricated from a high nickel alloy steel, one having a nickel content of approximately 35.5 percent and having a sufficiently low coeificient of contraction (approximately zero percent) to be characterized as being effectively dimensionally stable. More specifically, such an alloy steel is commercially available under the trade name Invar from the International Nickel Co., Inc., and has an ultimate strength of 100,000 p.s.i. Of prime importance for its use in the contemplated cryogenic applications in which severe temperature gradients are encountered through the walls of the container and between laden and unladen conditions, the thermal stress induced in Invar materials for a temperature variation from ambient of 350 F. is approximately 5,000 p.s.i. which is only five percent of its ultimate strength and well below its yield point. The Invar triplex panels are advantageously approximately four feet by twenty-five feet (the former dimension being dictated by the widths of Invar sheet stock commercially available) and include Invar sheets 32, 33 of .025 inch thickness.

In accordance with an important aspect of the invention, the triplex primary barrier panels 30 are firmly and fixedly anchored to the secondary insulating barrier 13, in a general end-to-end, side-by-side array without the employment of any expansion joints or the like, such as have been commonly employed heretofore in cryogenic containers of this type. To that end and in accordance with the present invention, selected panels and plug pieces of the dimensionally stable insulating barrier 13 include moldedin, tapped Invar anchor blocks 36 to which the outer flanges 37 (which advantageously may be overlapped and interlocking as shown) of the frame members are tightly fastened by Invar bolts 40. Furthermore and as an important aspect of the invention, the mounting of the triplex panels to the underlying secondary barrier 13 is made more secure by the inclusion of a continuous layer of adhesive sealant 45, such as epoxy, therebetween, which layer constitutes an intermediate liquid-tight barrier, enhancing the safety and reliability of the container 9.

As another important aspect of the invention, the inner Invar sheets 33 include flap portions 41 extending beyond the periphery of the frame 31 at two or more edges thereof. The flap portions, which advantageously are flexible before final assembly, may be infolded during the installation and alignment of the triplex panels upon the secondary barrier to facilitate the same. Thereafter, the flap portions 41 may be unfolded into overlapping relation with adjacent panels. The overlapped Invar sheets are Welded together as shown at 42 and, as should be understood, thereby define a continuous, effectively dimensionally stable primary barrier 15.

In accordance with a further important aspect of the invention, the honeycomb structure 34 is provided with a series of perforations or orifices 46 in communication with ports 47 formed in opposite web portions 39 of the frame 31. As will be appreciated, each of the triplex panels 30 thus provides a continuous passage therethrough, which passage directly communicates with the passages formed in the adjacent triplex panel to establish, in accordance with the inventive principles, a leakage detection network. A gas detector 48 is directly linked with the established detection network, through piping 49 and an opening 50 formed in the primary barrier, for the immediate sensing of cargo in the detection network.

The new and improved cryogenic container possesses an unusually great degree of fail safety. The direct mounting of dimensionally stable primary and secondary barrier panels, with an interposed liquid-tight barrier, ensures that a failure in one barrier will not result in the failure of the other. Moreover, the novel gas detection system, employing individual primary barrier panels as conduits in a detection network, enhances the safety and reliability of the complete system.

As may be appreciated, construction of a cryogenic insulating container, in accordance with the invention, is greatly simplified and extremely economical. A secondary barrier is established in a progressive fashion from the prefabricated insulating panels and, then, the prefabricated primary barrier panels are progressively anchored thereto by bolts and an intermediate epoxy barrier, to establish generally a primary barrier. Thereafter, completion of the primary barrier and the container may be accomplished with relative ease by uniting the flap portions of the Invar primary barrier panels to adjacent panels. An should be understood, the employment of dimensionally stable panels for both the primary and secondary barriers of a cryogenic insulation system is of extreme importance and results in significant savings of material and labor through the elimination of expansion joints and the problems associated with their installation.

It should be understood that the specific structure herein illustrated and described is intended to be representative only, as certain changes may be made therein without departing from the clear teachings of the disclosure. Accordingly, reference should be made to the following appended claims in determining the full scope of the invention.

What is claimed is:

1. An insulating container for liquefied natural gas including (a) a rigid support structure,

(b) a plurality of effectively dimensionally stable thermal insulating panels arrayed in a general endtO-end, side-by-side relation,

(c) means securing said insulating panels to said support in a manner whereby said panels define a continuous, liquid-tight secondary barrier,

(d) a plurality of triplex gas-resistant panels,

(e) each of said triplex panels including a peripheral frame member and inner and outer sheet members sandwiching a honeycomb core therebetween,

(f) said triplex panels being effectively dimensionally stable when subjected to cryogenic temperatures,

(g) said inner sheet members including flap portions extending beyond the peripheries ofsaid frame members and overlapping portions of the inner sheet members of adjacent triplex panels,

(h) dimensionally stable anchoring means securing said frame members of said triplex panels to said secondary barrier,

(i) adhesive means at the interfaces of said insulating and triplex panels and defining a continuous, liquidtight intermediate barrier therebetween,

(j) bonding means uniting said flap portions to adjacent ones of said inner sheet members whereby said members define a continuous substantially planer, liquid-tight primary barrier.

2. A container in accordance with claim 1, in which (a) said frame, sheet members and dimensionally stable mounting means are high nickel alloy steel, and

(b) said honeycomb structure is made from a material selected from the group of phenolic impregnated paper, fiberglas reinforced polyester, and aluminum.

3. An insulated wall for a cryogenic insulation system including (a) a rigid outer supporting structure,

(b) a plurality of effectively dimensionally stable insulating panels,

(c) means mounting said insulating panels to said supporting structure in an end-to-end, side-by-side array whereby said insulating panels define a cryogenic liquid-tight secondary barrier,

(d) a plurality of effectively dimensionally stable triplex panels including spaced apart sheet members supported by peripheral frame elements and sandwiching phenolic impregnated paper honeycomb core structures therebetween, said core structures defining a plurality of orifices therein,

(e) said frame elements including inner and outer peripheral flanges, said frame elements defining openings therein cooperating with said orifices to define a continuous gas passage through said triplex panels,

(f) anchoring means cooperating with said outer flanges and fixedly securing said triplex panels to said secondary barrier, and

(g) dimensionally stable sheet means interconnecting said inner flanges whereby said interconnected triplex panels define a cryogenic liquid-tight, dimensionally stable, primary barrier superimposed upon and fixed to said dimensionally stable secondary barrier, and gas detecting means operatively associated with said gas passage adapted to detect leakage of gas through said sheet means.

4. An insulated wall structure in accordance with claim 3, in which (a) a continuous layer of epoxy is interposed between said primary and secondary barriers and constitutes an intermediate liquid-tight barrier.

5. An insulated wall structure in accordance with claim 3, in which (a) said anchoring means includes high nickel alloy steel block molded into said secondary barrier and high nickel alloy steel bolts associated therewith.

6. An insulating container for liquefied natural gas including (a) a rigid support structure,

(b) a plurality of effectively dimensionally stable thermal insulating panels arrayed in a general endto-end, side-by-side relation,

(c) means securing said insulating panels to said support in a manner whereby said panels define a continuous, liquid-tight secondary barrier,

(d) a plurality of triplex gas-resistant panels,

(e) each of said triplex panels including a peripheral frame member and inner and outer sheet members sandwiching a honeycomb core therebetween,

(f) said triplex panels being effectively dimensionally stable when subjected to cryogenic temperatures, (g) said inner sheet members including flap portions extending beyond the peripheries of said frame members and overlapping portions of the inner sheet members of adjacent triplex panels,

(h) dimensionally stable anchoring means securing said frame members of said triplex panels to said secondary barrier,

(i) adhesive means at the interfaces of said insulating and triplex panels and defining a continuous, liquidtight intermediate barrier therebetween,

(j) bonding means uniting adjacent inner sheet members whereby said members define a continuous, liquid-tight primary barrier,

(k) said frame members define ports therein at opposite sides thereof,

(I) said honeycomb structures define passages therethrough and in communication with said ports,

(m) said passages of said triplex panels cooperating to define a leakage detection network, and

(n) a gas sensing means is associated with said network and adapted to detect the presence of gas therein.

7. An insulating container for liquefied natural gas including (a) a rigid support structure,

(b) a plurality of effectively dimensionally stable thermal insulating panels arrayed in a general endto-end, side-by-side relation, said insulating panels comprising glass fiber reinforced polyester shells filled with polyurethane,

(c) means securing said insulating panels to said support in a manner whereby said panels define a continous, liquid-tight secondary barrier,

(d) a plurality of triplex gas-resistant panels,

(e) each of said triplex panels including a peripheral frame member and inner and outer sheet members sandwiching a honeycomb core therebetween,

(f) said triplex panels being effectively dimensionally stable when subjected to cryogenic temperatures, (g) said inner sheet members including flap portions extending beyond the peripheries of said frame members and overlapping portions of the inner sheet members of adjacent triplex panels,

(h) dimensionally stable anchoring means securing said frame members of said triplex panels to said secondary barrier,

(i) adhesive means at the interfaces of said insulating and triplex panels and defining a continuous, liquidtight intermediate barrier therebetween,

(j) bonding means uniting adjacent inner sheet members whereby said members define a continuous, liquid-tight primary barrier.

8. A system of primary barrier panels for use in a cryogenic insulating structure, said structure including insulating secondary barrier panels, wherein each of said primary barrier panels comprises in combination:

(a) a rectangular frame member having a C-shaped cross-section fabricated from extruded high nickel alloy steel,

(b) said frame having peripheral inner and outer flanges and an intermediate web,

(c) a pair of spaced inner and outer sheets of high nickel alloy steel bonded to said inner and outer flanges,

(d) a honeycomb core structure sandwiched between said sheets,

(e) said inner sheets having flap portions extending beyond the periphery of said frame,

(f) means for continuously bonding said outer sheets of said primary barrier to said secondary barrier panels, and

(g) second bonding means for uniting said flap portions to the inner sheet members on adjacent ones of said primary barrier panels whereby said flap portions and said inner sheet members define a continuous, substantially planar, effectively dimensionally stable, liquid-tight primary barrier.

References Cited UNITED STATES PATENTS 2,708,774 5/1955 Seelen 220 2.1 2,728,702 12/1955 Simon etal 220 9 2,744,042 5/1956 Pace 220 9 2,772,860 12/1956 Nelson 22063 2,980,279 4/1961 Lueders 220 9 2,983,401 5/1961 Murphy 220 10 3,030,669 4/1962 Dosker 220 10 3,031,856 5/1962 Wiedemann et al. 220 9 3,150,793 9/1964 Messer 220 9 3,158,383 11/1964 Anderson etal 220 9 3,158,459 11/1964 Guilhem 220 15 3,189,211 6/1965 Podlaseck 220 9 3,273,740 9/1966 Herrenschmidt 220 9 THERON E. CONDON, Primary Examiner.

JAMES R. GARRETT, Examiner. 

1. AN INSULATING CONTAINER FOR LIQUEFIED NATURAL GAS INCLUDING (A) A RIGID SUPPORTED STRUCTURE, (B) A PLURALITY OF EFFECTIVELY DIMENSIONALLY STABLE THERMAL INSULATING PANELS ARRAYED IN A GENERAL ENDTO-END, SIDE-BY-SIDE RELATION, (C) MEANS SECURING SAID INSULATING PANELS TO SAID SUPPORT IN A MANNER WHEREBY SAID PANELS DEFINE A CONTINUOUS, LIQUID-TIGHT SECONDARY BARRIER, (D) A PLURALITY OF TRIPLEX GAS-RESISTANT PANELS, (E) EACH OF SAID TRIPLEX PANELS INCLUDING A PERIPHERAL FRAME MEMBER AND INNER AND OUTER SHEET MEMBERS SANDWICHING A HONEYCOMB CORE THEREBETWEEN, (F) SAID TRIPLEX PANELS BEING EFFECTIVELY DIMENSIONALLY STABLE WHEN SUBJECTED TO CRYOGENIC TEMPERATURES, 